The present invention relates to fasteners and more particularly to fasteners having a head configuration which is configured so as to prevent unauthorized removal thereof.
Heretofore a wide variety of prior art head designs have been disclosed relative to tamperproof features. Many of these designs incorporate internal driving recesses configured to accept only a specially configured tool. A wide variety of head styles using an internal driving surface provide rotary inducing abutment surfaces only in the tightening direction with camming surfaces extending in the direction which would tend to remove the fastener. The use of internal driving recesses generally requires a head with a certain volume of material and are typically conically shaped to provide the necessary volume. In order to provide the proper abutting surfaces for high torque conditions, prior art tamperproof systems require a head with a high profile if they are of the flat bearing surface variety. The presence of any high profile screw offers the possibility that a tight clamping or wrenching can be obtained on the periphery of the head, thus leading to an unauthorized removal.
Other disadvantages of the prior art tamperproof fasteners reside in the inability to critically center a driving tool on the fastener so that the tool is not inclined relative to the axis of the fastener. This becomes important when relatively low or small abutment surfaces are relied upon on the fastener head to transmit high torque.